This invention relates generally to apparatus for reproducing an information signal from a rotating disc on which the information signal is recorded in a spiral signal path defining record tracks, such as a digital audio disc, and more particularly is directed to improvements in a disc player of the type adapted to perform a small scale track jump operation repeatedly during the fast forwarding or fast reversing mode in which the reading position by a pick-up device is moved rapidly in the forward or reverse direction transverse to record tracks defined by successive turns of a spiral signal path on a disc.
As for an optical record disc such as a digital audio disc, an information signal such as an audio signal is recorded in a spiral signal path defining record tracks so as to be optically readable with, for example, an alignment of pits. When the information signal recorded on such an optical record disc is reproduced by a disc player, the optical record disc is rotated in such a manner as to keep the tangential velocity of the spiral signal path at a reading position by a pick-up device provided in the disc player (hereinafter referred as to the scanning velocity) constant at a predetermined value and the record tracks defined by successive turns of the spiral signal path on the optical record disc are scanned in turn by a light beam emitted from the pick-up device to determine the reading position so that the information signal is read from the record tracks by the pick-up device. In the case of the digital audio disc, generally, the information signal is recorded along the spiral signal path thereon in the direction from the innermost turn to the outermost turn and, in reproducing the information signal from the digital audio disc, the reading position by the pick-up device of the disc player is shifted gradually in the radial direction on the digital audio disc from the innermost radius to the outermost radius so as to obtain a correct reproduced information signal.
When a specific portion of the information signal recorded on the record disc is selectively reproduced by the disc player, the disc player is operative in the fast forwarding or reversing mode in which the reading position by the pick-up device on the record disc is moved rapidly in the direction transverse to the record tracks in order to shift the reading position by the pick-up device to a location where the specific portion of the information signal is recorded prior to the reading operation thereof. During such fast forwarding or reversing mode the disc player performs repeatedly a track jump operation in which the reading position by the pick-up device is controlled to move rapidly in the direction transverse to the record tracks to a record track which is located a number of tracks away from the record track at which the reading position of the pick-up device is presently situated. In such a case, the disc player is operative in the normal reproducing mode in which the information signal including address data or the like are read from the record track by the pick-up device for a predetermined short period whenever the track jump operation has been carried out once and then performs the next track jump operation, so that the track jump operation is performed repeatedly at intervals of the predetermined period.
In the fast forwarding mode, the reading position by the pick-up device on the record disc is rapidly moved in a forward direction defined by the direction of movement of the reading position by the pick-up device on the record disc in the normal reproducing mode, and in the fast reversing mode, the reading position by the pick-up device on the disc is rapidly moved in a reverse direction opposite to the forward direction. In relation to a record disc on which the information signal is recorded along the spiral signal path thereon in the direction from the innermost turn to the outermost turn, such as the digital audio disc, the forward direction coincides with the radial direction from the innermost radius to the outermost radius thereon.
In the disc player as mentioned above, there has arisen that a substantial moving distance measured along the spiral signal path in respect of the reading position by the pick-up device moved for a certain period in the fast forwarding mode is different from a substantial moving distance measured along the spiral signal path in respect of the reading position by the pick-up device moved for the same certain period in the fast reversing mode, and such a difference in substantial moving distance is especially remarkable in case that a small scale track jump operation, such as one track jump operation in which the reading position by the pick-up device is rapidly moved to an adjoining record track from the record track at which the reading position by the pick-up device is presently situated, is repeatedly performed during the fast forwarding or reversing mode. This results in the disadvantage that the moving speed of the reading position by the pick-up device in the fast forwarding mode is substantially higher than that in the fast reversing mode.
Referring now to FIGS. 1 and 2, the difference in substantial moving distance as above mentioned will be explained in detail hereinafter.
FIG. 1 shows the positional relation between the spiral signal path defining the record tracks on the record disc and the reading position by the pick-up device in the fast forwarding or reversing mode taken in the previously proposed disc player. Since the record disc is rotated at a predetermined constant scanning velocity, each one turn of the record disc spends different time depending on the reading position by the pick-up device on the record disc. For example, the time necessary for one turn of the record disc in the situation in which the reading position by the pick-up device is located at the innermost turn of the spiral signal path is about 130 msec. and the time for necessary for one turn of the record track in the situation in which the reading position by the pick-up device is located at the outermost turn of the spiral signal path is about 290 msec. Record tracks L.sub.a, L.sub.b and L.sub.c shown in FIG. 1 are positioned at such an area on the record disc that the time for one turn of the record disc with the reading position by the pick-up device located thereat is about 200 msec., and the record disc is rotated in the direction indicated by an arrow R.
When the one track jump operation is repeatedly performed at intervals of the period of 100 msec. in regard to the record tracks L.sub.a, L.sub.b and L.sub.c in the fast forwarding mode, by the first one track jump operation the reading position by the pick-up device is quickly moved, for example, from a point a on the record track L.sub.a to a point b on the record track L.sub.b which is adjoining outside to the record track L.sub.a, and then the reading position by the pick-up device is controlled to trace the record track L.sub.b from the point b to a point c thereon under the operation in the normal reproducing mode, so that the information signal is read from the record track L.sub.b. Next to this, the second one track jump operation is performed so that the reading position by the pick-up device is quickly moved from the point c to a point d on the record track L.sub.c which is adjoining outside to the record track L.sub.b and then controlled to trace the record track L.sub.c from the point d under the operation in the normal reproducing mode. After that, the one track jump operation is repeatedly performed at intervals of the reading period under the operation in the normal reproducing mode in the same manner as mentioned above, so that the reading position by the pick-up device is rapidly moved repeatedly at a track by track basis in the direction to the outermost turn of the spiral signal path on the record disc.
On the other hand, when the one track jump operation is repeatedly performed at intervals of the period of 100 msec. in regard to the record tracks L.sub.a, L.sub.b and L.sub.c in the fast reversing mode, by the first one track operation the reading position by the pick-up device is quickly moved, for example, from a point e on the record track L.sub.b to a point f on the record track L.sub.a which is adjoining inside to the record track L.sub.b, and then the reading position by the pick-up device is controlled to trace the record track L.sub.a from the point f to a point g thereon under the operation in the normal reproducing mode, so that the information signal is read from the track L.sub.a. Next to this, the second one track jump operation is performed so that the reading position by the pick-up device is quickly moved from the point g to a point h on the record track which is adjoining inside to the record track L.sub.a and then controlled to trace the record track on which the point h is located under the operation in the normal reproducing mode. After that, the one track jump operation is repeatedly performed at intervals of the reading period under the operation in the normal reproducing mode in the same manner as mentioned above, so that the reading position by the pick-up device is rapidly moved repeatedly at a track by track basis in the direction to the innermost turn of the spiral signal path on the record disc.
FIGS. 2A and 2B show the movement of the reading position by the pick-up device which is moved by the above mentioned one track jump operation performed repeatedly during the fast forwarding mode and the fast reversing mode, respectively. In each of FIGS. 2A and 2B, the ordinate represents the time and the abscissa represents the distance measured along the spiral signal path on the record disc. Further, in FIGS. 2A and 2B, T.sub.1 represents the period of the one track jump operation, that is, 100 msec. in this example and W.sub.1 represents the length of one turn of the spiral signal path defining each of the record tracks L.sub.a, L.sub.b and L.sub.c which are approximated hereon to have the same length.
Referring to FIGS. 2A and 2B, in the case of the fast forwarding mode, when the reading position by the pick-up device is quickly moved to the point b from the point a by the first one track jump operation, the substantial moving distance measured forward along the spiral signal path in respect of the reading position by the pick-up device corresponds to W.sub.1 as shown with a soled line from a to b in FIG. 2A. Since the time necessary for performing the one track jump operation once is so short as to be negligible, the succeeding reading period in which the reading position by the pick-up device is controlled under the operation in the normal reproducing mode corresponds approximately to the period T.sub.1 equal to 100 msec. Accordingly, the substantial moving distance measured forward along the spiral signal path in respect of the reading position by the pick-up device during the reading period before the second one track jump operation corresponds to a half of W.sub.1, that is, 1/2W.sub.1 as shown with a broken line from b to c in FIG. 2A. After that, a further substantial moving distance measured forward along the spiral signal path in respect of the reading position by the pick-up device is obtained in the same manner in consequence of the second one track jump operation and other operation successive thereto, in turn. Consequently, the substantial moving distance measured forward along the spiral signal path in respect of the reading position by the pick-up device during each period T.sub.1 corresponds to one and half turns of the spiral signal path at the area wherein the record tracks L.sub.a, L.sub.b and L.sub.c are positioned, that is, 3/2W.sub.1.
To the contrary, in the case of the fast reversing mode, when the reading position by the pick-up device is quickly moved to the point f from the point e by the first one track jump operation, the substantial moving distance measured backward along the spiral signal path in respect of the reading position by the pick-up device corresponds to W.sub.1 as shown with a solid line from e to f in FIG. 2B. Then, the substantial moving distance measured forward along the spiral signal path in respect of the reading position by the pick-up device during the succeeding reading period, in which the reading position by the pick-up device is controlled under the operation in the normal reproducing mode, corresponds to a half of W.sub.1, that is, 1/2W.sub.1 as shown with a broken line from f to g in FIG. 2B. After that, a further substantial moving distance measured backward or forward along the spiral signal path in respect of the reading position by the pick-up device is obtained in the same manner in consequence of each of the second one track jump operation and other operation successive thereto. Consequently, in this case, the substantial moving distance measured backward along the spiral signal path in respect of the reading position by the pick-up device during each period T.sub.1 corresponds to a half turn of the spiral signal path at the area wherein the record tracks L.sub.a, L.sub.b and L.sub.c are positioned, that is, 1/2W.sub.1.
As described above, in case that the one track jump operation is repeatedly performed during the fast forwarding or reversing mode, a difference corresponding to one turn of the spiral signal path is made between the substantial moving distance measured along the spiral signal path in respect of the reading position by the pick-up device moved for a period of the one track jump operation in the fast forwarding mode and the substantial moving distance similarly measured in the fast reversing mode. This results from that the reading position by the pick-up device is controlled to trace forward the spiral signal path in the normal reproducing mode after each track jump operation in both the fast forwarding mode and the fast reversing mode. Accordingly, in case that a large scale track jump operation, such as a hundred track jump operation in which the reading position by the pick-up device is rapidly moved to traverse about one hundred of turns of the spiral signal path, is repeatedly performed during the fast forwarding or reversing mode, such a difference in substantial moving distance measured along the spiral signal path in respect of the reading position by the pick-up device is inconspicuous.